Drive Scheme for Weakly Coupled Coils

ABSTRACT

A variable efficiency and response buck converter is achieved. The device includes a multi-phase switch, the coupled coils, the filter capacitor, and the load. The multi-phase switch includes the phase control inputs, the circuit common reference, at least two pairs of complementary switches with each switch containing one upper switch and one lower switch, at least two phase control outputs from the complementary switches. The coupled inductive coils are coupled to the phase control outputs to enable weak couplings and strong couplings. Based on the working mode, equivalently the coupled coils can provide strong mutual inductances and weak mutual inductances. The filter capacitors connected to the output of the coupled coils provide high efficiency output to the load.

This is a divisional application of U.S. patent application Ser. No.14/262,971 filed on Apr. 28, 2014, which is herein incorporated byreference in its entirety, and assigned to a common assignee.

FIELD

The disclosure relates generally to variable buck converters, voltageregulators, and methods and, more particularly, to how to control theefficiency and the response of the buck converter and voltage regulatorsand a method thereof.

BACKGROUND

Buck converters are switching voltage regulators that operate in a stepdown method to provide a voltage output that is smaller than the inputvoltage. It accomplishes this by causing the circuit topology to changeby virtue of turning on and off semiconductor devices. It uses signalswitching to transfer energies into inductors. It uses a low pass filterscheme to eliminate high frequency harmonics to maintain a relativelyconstant output voltage and reduce the ripple of the output.

Typically buck converters use a feedback circuit to regulate the outputvoltage in the presence of load changes. They are more efficient at thecost of additional components and complexity.

Buck converters can be made very compact. Therefore they are popularlyused for mobile devices, printed circuit boards, even in integratedcircuit packages.

An example of a prior art buck converter circuit 600 is illustrated in acircuit schematic block diagram in FIG. 6a . The circuit 600 includesthe a P type switch SW1 612, an N type switch SW2 614, an energy storageinductor L 630, the low pass filter capacitor C_(F) 632, and the outputload R_(L) 634. The input voltage Vin 610 is the given high voltage. Theoutput voltage Vout 636 is the converted voltage that is usually lowerthan Vin 610. The Vcom 640 is the common reference ground of the buckconverter circuit 600. The control voltage V_(GS1) 616 is coupled to thegate of the switch SW1 612 to control its on and off status. The controlvoltage V_(GS2) 618 is coupled to the gate of the switch SW2 614 tocontrol its on and off status.

The control voltage V_(GS1) 616 and V_(GS2) 618 are complementary toeach other. It means that when V_(GS1) 616 turns on the switch SW1 612,the V_(GS2) 618 turns off the switch SW2 614. When V_(GS1) 616 turns offthe switch SW1 612, the V_(GS2) 618 turns one the switch SW2 614. Hence,there are two working states for the buck converter in one workingcycle.

One example of the working cycle is illustrated in FIG. 6b . During thetime period T_(s1) 662, the switch SW1 612 is turned on. Then the switchSW2 614 is turned off. The node voltage Vs 620 is equal to the inputvoltage Vin 610 since the SW1 612 is on with almost zero voltage drop.Then the buck converter storing the magnetic energy into the inductivecoil charges inductor L 630. Then during the time period T_(s2) 663, theswitch SW1 612 is turned off. Base on the Lenz's law, the inductor L 630will instantaneously maintain the current flowing through it. Thereforthe loop current will go through the switch SW2 614 and turn it on. Thenode voltage Vs 620 is shorted to the common reference Vcom 640. Thetotal working cycle is T_(sw) 666. It is obvious thatT_(sw)=T_(s1)+T_(s2). The inductor and the capacitor form the low passfilter that filters out the high frequency harmonics reaches the outputVout 636. As a result, the output voltage Vout 636 is relativelyconstant with very small ripples.

If the ratio of T_(s1) over T_(sw) is defined as the duty cycle D,D=T_(s1)/T_(sw). During the period T_(s1) 662, the current through theinductor 630 L ramps up linearly. During the period T_(s2) 664, thecurrent through the inductor 630 L ramps down linearly. To make sure theending current of the ramping down is equal to the starting current ofthe ramping up so that the buck converter 600 can maintain balance, theratio of the output Vout 636 to the input voltage Vin 610 must be equalto the duty cycle:

Vout/Vin=D

The output voltage Vout 636 can be further controlled through feedbackschemes. One popular method is the pulse width modulation (PWM) method.The PWM mode operates switches in synchronization with a clock that hasa predetermined cycle. The magnetic energy stored in the inductor isrepeatedly increased and decreased periodically. Hence, the power istransferred from the input Vin 610 to the output Vout 636. The outputcan be stabilized to a desired level by turning on and off the switchduring synchronization with the clock. This mode is optimal for mid andhigh load current. However, it is not very efficient at lower loadcurrents. Then if a buck converter 600 is to operate efficiently over arelatively wide range of load currents, including low load currents, thepulse frequency modulation (PFM) will be used.

The PFM is similar to PWM in the sense that the switch SW1 612 can beused to produce a series of inductor current pulses that are applied tothe filter capacitor C_(F) 632. However, the frequency of the pulses isnot fixed. It varies in order to maintain a regulated output voltagebetween the upper regulated output voltage level and the lower regulatedvoltage level. At low load currents, PFM can provide increasedefficiency as compared to PWM for the same current output. This isparticularly true since the PWM operation has been optimized forefficient mid and high load current operation.

In view of the foregoing, buck converters have been designed to operatein a PWM mode for mid and high load currents and PFM for low loadcurrents.

It is commonly known that a smaller inductor L 630 in the buck converter600 give faster transient response, and the larger inductors give higherefficiency. High efficiency is important in all modes. But the linkbetween the inductance of the inductor L 630 and the efficiency isparticularly critical in the pulsed frequency modulation (PFM) mode.Fast load transient response on the other hand is most important inmodes optimized for high load currents that can be handled by the pulsewidth modulation modes (PWM).

Inductors are just becoming available where several coils are embeddedin the same package. These differ from those previously available inthat their coupling ratio is much lower. Traditional multi-inductorpackages were designed for use as transformers. Therefore they have acoupling ratio approaching 100%. However, with the new manufacturingtechniques, multi-inductor packages are available where the couplingratio is around 10%.

SUMMARY

If the buck converter is designed to make use of multi-inductorpackages, driving the inductors with the correct architecture can bringbenefits to both efficiency and load transient response.

It is known that small value inductors allow faster responses to theload current changes because the current variation rate dI/dt isproportional to L. Large value inductors are more efficient for a numberof reasons. In PFM mode, the charge delivered to the output is fixed percycle (for discontinuous mode). The energy wasted can also be assumed tobe fixed per cycle. Anything that increases the charge delivered(without increasing the energy wasted) will increase the efficiency. Ahigher value inductor increases the charge delivered as it slows downthe current ramp and increases the area under the current ramp curve.

It has been found that traditionally the load transient response (speed)and efficiency were mutually exclusive. The fast load transient responseis achieved by the required small inductors. The higher efficiency isachieved by the large value inductors. The buck converter mustcompromise on one of the requirements. As will become clear in thefollowing Description of the disclosure, using weakly coupled inductors,where they are in a single package, or simply deliberately coupled bytheir layout, the buck converter can make the most of both speed andefficiency simultaneously.

A principal object of the present disclosure is to provide a switchconverter.

A further object of the present disclosure is to provide a variableefficiency and transient response voltage conversion circuit device

Another further object of the present disclosure is to provide a methoda method to tune the inductance of the mutually coupled inductor coilsto provide a lower inductance for fast converter response or a higherinductance for suppression of current ripples.

In accordance with the objects of this disclosure, a switch converter isachieved. The device comprises a multi-phase switch having an inputvoltage, mutually coupled inductive coils connected to the multi-phaseswitch, wherein the switching converter is capable of tuning theinductance of the mutually coupled inductor coils to provide a lowerinductance for fast converter response or a higher inductance forsuppression of current ripple. The multi-phase switch is capable ofreceiving phase control signals and transferring them into phases neededfor sync modes and sleep modes. It comprises at least two pairs ofcomplementary signals as the input to multi-phase switches, at least twopairs of complementary switches receiving complementary signals asinputs to generate sync mode or sleep mode complementary phases, and atleast one pair of phase signals generated as the output fromcomplementary switches. The two pairs of complementary signals arecapable of generating the sleep mode phase when they are in phases (0°)and the sync mode phase when they are out-of-phase (180°). The pair ofoutput phase signals are instantiated in pairs, such as 0°, 90°, 180°,270° for 4 pairs of complementary input signals. The mutually coupledinductive coil connected to output phase signals of multi-phase switchesis capable of enabling both strong and weak couplings to optimizeefficiencies and speed requirements of switches, the mutually coupledinductive coil further comprises 2 inductors with mutual couplings for0° and 180° phases, or 4 inductors with mutual couplings for 0°, 90°,180°, 270°, or multi-inductors with more phases. The mutually coupledinductive coil connected to output phase signals of multi-phase switcheshas the coupling ratio less than 100%. The mutually coupled inductivecoil connected to output phase signals of multi-phase switches has thecoupling ratio in between 5% and 30%. The mutually coupled inductivecoil connected to output phase signals of multi-phase switches has abigger inductance when the phase signal is in the sleep mode and asmaller inductance when the phase signal is in the sync mode. Thecoupled inductive coil connected to output phase signals of multi-phaseswitches in the sleep mode has 1% higher efficiency for low outputcurrents. The coupled inductive coil connected to output phase signalsof multi-phase switches in the sync mode has faster response for highoutput currents.

Also In accordance with the objects of this disclosure, a variableefficiency and transient response voltage conversion circuit device isachieved. The device comprises a converter control unit, an array ofphase control circuit units controlled by the converter control unit, amulti-phase switch controlled by the array of phase control circuitunits, a mutually coupled inductive coil at the output of themulti-phase switch, a plurality of capacitors and resistors circuits atthe output of the coupled inductive coil; and an output monitor circuitconnected to the output of the plurality of capacitors and resistorscircuits and the input of the converter control unit. The convertercontrol unit is capable of receiving control commands and transferringthem into phase control signals needed for phase control circuits. Theconverter control unit further comprises circuit accepting controlsignals for efficiency and response specifications, and a regulationcircuit accepting signals from the output monitor circuit. The array ofphase control units connected to the control unit is capable ofconverting signals from outputs of the control unit to analogcomplementary control signals. Each phase control circuit unit furthercomprises a circuit accepting control signals from the converter controlunit, and a conversion circuit with certain embedded algorithms toimplement complementary phase control signals. The multi-phase switchcontrolled by the array of phase control circuit units is capable ofcreating an array of complementary phase signals that enables sleepmodes, sync modes, or other multi-phase modes according to the number ofinput complementary phase control signals. A multi-phase switch furthercomprises at least two pairs of complementary signals as the input tomulti-phase switches, at least two pairs of complementary switchesreceiving complementary signals as inputs to generate sync mode or sleepmode complementary phases, and at least one pair of phase signalsgenerated as the output from complementary switches. The mutuallycoupled inductive coil connected to output phase signals of multi-phaseswitches is capable of enabling both strong and weak couplings tooptimize efficiencies and speed requirements of switches. The mutuallycoupled inductive coil further comprises 2 inductors with mutualcouplings for 0° and 180° phases, or 4 inductors with mutual couplingsfor 0°, 90°, 180°, 270°, or multi-inductors with more phases. Theplurality of capacitors and resistors circuits at an output of thecoupled inductive coil is capable of filtering out high frequencyharmonics to deliver relatively constant voltages. A plurality ofcapacitors and resistors circuits further comprises a plurality ofcapacitors shunt in between the output and the common reference, aplurality of resistors shunt in between the output and the commonreference, or a plurality of capacitors and resistors shunt in betweenthe output and the common reference. The output monitor circuitconnected to the output of the plurality of capacitors and resistorscircuits and the input of the converter control unit is capable ofdetecting the load voltage or current and feed back the control signalinto the control unit for the pulse frequency modulation (PFM) or thepulse width modulation (PWM). The output monitor circuit furthercomprises a high impedance receiving circuit to sample the load currentor voltage, a signal conversion circuit with embedded algorithms totransfer the sampled load current or voltage into control signals, andan output driving circuit to port the generated port signal into theconverter control unit to facilitate the pulse frequency modulation(PFM) or the pulse width modulation (PWM).

Also in accordance with the objects of this disclosure, a method forcontrolling inductance of a switch converter is achieved. The methodcomprises a multi-phase switch having an input voltage, mutually coupledinductive coils connected to the multi-phase switch; and tunes theinductance of the mutually coupled inductor coils to the provide a lowerinductance for fast converter response or a higher inductance forsuppression of current ripple. The multi-phase switch comprisescomplementary switches with complementary input voltages to generatedoutput signals with various controlled phases. The mutually coupledinductive coils comprise weakly two or more coupled coils connected tothe output of the multi-phase switches. The bigger effective inductancesare obtained by controlling input phases of the coupled inductance coilsto be in phase and bigger effective inductances are obtained bycontrolling input phases of the coupled inductance coils to beout-of-phase. The buck works in the “sleep mode” when the input phasesof the coupled inductive coils are in phase and in the “sync mode” whenthe input phases of the coupled inductive coils are out of phase. Theefficiency under the “sleep mode” is highest while the load responseunder the “sync mode” is the fastest. The efficiency under the “syncmode” does not matter much at large load current due to the weakcoupling of the inductive coils. The method can be extended to othertype of bucks such as boosts and buck-boosts.

As such, a novel variable efficiency and response buck converter withthe controlled effective inductance from the coupled coils and a methodto vary the efficiency and the response needed for the voltageconversion circuit through the weakly coupled coils are hereindescribed. The circuit provides various efficiencies and response speedto the load. The efficiency is achieved with the larger effectiveinductance from the weakly coupled inductive coils. The faster responseis achieved with the smaller effective inductance from the weaklycoupled inductive coils. The device and method are applicable to avariety of switching converters, including buck converters, boostconverters and buck-boost converters. The device and method areapplicable to a variety of phase control schemes, the pulse frequencymodulation (PFM), and the pulse width modulation (PWM) methods. Thedevice and method are extensible to add more pairs of weakly coupledcoils. The device and method are extensible to use strongly coupledcoils. Other advantages will be recognized by those of ordinary skillsin the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure and the corresponding advantages and featuresprovided thereby will be best understood and appreciated upon review ofthe following detailed description of the disclosure, taken inconjunction with the following drawings, where like numerals representlike elements, in which:

FIG. 1 is a circuit schematic diagram illustrating one example of avariable efficiency and transient response buck converter in accordancewith one embodiment of the disclosure;

FIG. 2 is a circuit schematic diagram illustrating one example of avariable efficiency and transient response buck converter with thefeedback circuit and the phase control system in accordance with oneembodiment of the disclosure;

FIG. 3 is the signal diagram illustrating one example of the inductorcoil currents in a variable efficiency and transient response buckconverter using the in-phase “sleep mode” in accordance with oneembodiment of the disclosure;

FIG. 4 is the signal diagram illustrating one example of the inductorcoil currents in a variable efficiency and transient response buckconverter using the out-of-phase “sync mode” in accordance with oneembodiment of the disclosure;

FIG. 5 is the efficiency diagram illustrating one example of a variableefficiency and transient response buck converter using the in-phase“sleep mode” and the out-of-phase “sync mode” in accordance with oneembodiment of the disclosure;

FIG. 6 is a circuit schematic block diagram illustrating a prior art,buck converter circuit.

FIG. 7 is the flow chart illustrating the methodology of using weaklycoupled inductive coils to tune both speed and efficiencysimultaneously.

DESCRIPTION

FIG. 1 is a circuit schematic diagram illustrating one example of avariable efficiency and response buck converter 100 in accordance withone embodiment of the disclosure. The device 100 includes a multi-phaseswitch 110, the coupled coils 140, the filter capacitor 150, and theload 164. The multi-phase switch 110 includes input Vin 112, the circuitcommon reference Vcom 114, the upper switch SW11 124, the low switchSW12 126, the upper switch SW21 128, the low switch SW22 130, the inputV_(GS11) 116, the input V_(GS12) 118, the input V_(GS21) 120, the inputV_(GS22) 122, the output 132 from the upper switch SW11 124 and the lowswitch SW12 126, and the output 134 from the upper switch SW21 128 andthe low switch SW22 130. The coupled coils 140 includes inductor L1 142,the inductor L2 144, the mutual inductance L12 146, the input 148 to theinductor L1 142, the input 149 to the inductance L2 149, the output 162.The filter capacitor 150 includes the filter capacitor C_(F) 152. Theload is simply represented by the load resistor R_(L) 164. The output ofthe buck converter is Vout 170.

In the multi-phase switches 110, the switch SW11 124 and SW12 126 form apair and are preferably coupled at the node 125. The switches may beimplemented in any available technology, such as MOS or bipolar or mixedtechnology. The input V_(GS11) 116 is preferably coupled to the switchSW11 124. The input V_(GS12) 118 is preferably coupled to the switchSW12 126. The output 132 is preferably coupled at the node 125 to boththe upper switch SW11 124 and the low switch SW12 126. The switch SW21128 and SW22 130 form a pair and are preferably coupled at the node 129.The switches may be implemented in any available technology, such as MOSor bipolar or mixed technology. The input V_(GS21) 120 is preferablycoupled to the switch SW21 128. The input V_(GS22) 122 is preferablycoupled to the switch SW22 130. The output 134 is preferably coupled atthe node 129 to both the upper switch SW21 128 and the low switch SW22130.

In the coupled coils 140, the input 148 is preferably coupled to theoutput 132 from the multi-phase switches 110, and the input 149 ispreferably coupled to the output 134 from the multi-phase switches 110.The inductor L1 142 is preferably coupled to the inductor L2 144 at thenode 145. The other end of inductor L1 142 is preferably coupled to theinput 148. The other end of inductor L2 144 is preferably coupled to theinput 149. The output 162 is preferably coupled to the coupled coils 140at the node 145.

In the filter capacitor 150, one side of the filter capacitor C_(F) 152is coupled to the input 162. The other side of the filter capacitorC_(F) 152 is coupled to the common reference ground Vcom 114. The output154 of the filter capacitor 150 is coupled to one side of the loadresistor R_(L) 164 at the node 160. The output Vout 170 is preferablycoupled to the load resistor R_(L) 164 at the node 160.

While the embodiment illustrates one coupled coils with only two pairsof switches, it should be understood that multiple coupled coils withmultiple pair of switches may be used in the present disclosure.

In the preferred embodiment, the input V_(GS11) 116 and the inputV_(GS12) 118 are controlled by complementary pulsed signals. Thereby theswitch SW11 124 has opposite on/off status relative to the SW12 126. Theinput V_(GS21) 120 and the input V_(GS22) 122 are controlled bycomplementary pulsed signals. Thereby the switch SW21 128 has oppositeon/off status relative to the SW22 130. Because the symmetry of thecircuit configuration in the multi-phase switches 110, the output 132and 134 from the multi-phase switches 110 will have identical waveformsexcept the phase. The output 132 and 134 could be in-phase orout-of-phase. When the output 132 and 134 are in-phase, the buckconverter 100 is working under the “sleep mode”. When the output 132 and134 are out-of-phase, the buck converter 100 is working under the “syncmode”. The sleep mode is a mode for the low output currents and highefficiency. It is preferably for the pulse frequency modulation (PFM).The sync mode is a mode for the larger load transients. It is preferablyfor the pulse width modulation (PWM).

The inductor L1 142 and L2 144 form a pair of inductors. They have themutual inductance L12 146. If the inductor L1 142 and L2 144 are weaklycoupled, the mutual inductance L12 146 is small. The current in theinductor L1 142 will affect the value of the current in the inductor L2144 if the mutual inductance L12 is not equal to zero. If the input 148of the inductor L1 142 and the input 149 of the inductor L2 144 arein-phase, both inductors are operated in the same polarity. Hence, thecurrent in the inductor L1 142 and the current in the inductor L2 144will both ramp with the same polarity. The coils will interfereconstructively. The current in the inductor L1 142 will act togetherwith the current in the inductor L2 144, and vice versa. Thisconstructive interference increases the effective inductance to the buckconverter 100. As one example, if the two inductors are matched andcoupled with 10% coupling ratio, the increase in the effectiveinductance is also 10%. If the input 148 of the inductor L1 142 and theinput 149 of the inductor L2 144 are out-of-phase, both inductors areoperated in the opposite polarity. Hence, the current in the inductor L1142 and the current in the inductor L2 144 will ramp with the oppositepolarity. The coils will interfere destructively. The current in theinductor L1 142 will act inversely with the current in the inductor L2144, and vice versa. This destructive interference decreases theeffective inductance to the buck converter 100.

In the proposed embodiment, the coupled coils can be implemented in thesame IC package. With the new manufacturing techniques, the weaklycoupled coils are available in package where the coupling ratio isaround 5% to 30%. It is also understandable that the proposed embodimentdoes not have a limit to the coupling ratio. Hence, coupled coils madeby other manufacturing techniques with strong inductive coupling arealso included in the proposed embodiment.

In the proposed embodiment, the buck converter 100 has at least twopairs of switches in the multi-phase switches 110. The switches SW11 124and the SW12 126 are one pair with the output 132. The switches SW21 128and the SW22 130 are another pair with the output 134. The inductor L1142 is controlled by the output 132. The inductor L2 144 is controlledby the output 134.

The buck converter 100 works in the “sleep mode” when the output 132 and134 are in-phase. In this case, if the current in the inductor L1 142ramps up, the current in the inductor L2 144 also ramps up. Hence, thecoupled coils 140 appear to have larger effective buck converterinductance than the nominal inductance value of each individual inductorL1 142 and L2 144. Because the larger buck inductance results in higherefficiency, the “sleep mode” will show higher efficiency, especially forthe low output currents in the PFM mode.

The buck converter 100 works in the “sync mode” when the output 132 and134 are out-of-phase. In this case, if the current in the inductor L1142 ramps up, the current in the inductor L2 144 ramps down. Hence, thecoupled coils 140 appear to have a smaller effective buck converterinductance than the nominal inductance value of each individual inductorL1 142 and L2 144. Because a smaller buck inductance allows the outputcurrent to change more rapidly in the response to a load step, the buckconverter 100 will have better load transient response, especially forthe larger load transient in the PWM mode. The efficiency in this modeis not typically limited by the coil value. Hence, the decrease in theefficiency caused by the smaller inductance value is negligible.

Referring now to FIG. 3, it is one example diagram of the currents inthe inductor L1 142 and inductor L2 144 in the “sleep mode” where highefficiency is needed. In this mode, the current Icoil (L1) 312 in theinductor L1 142 is in-phase with the current Icoil (L2) 322 in theinductor L2 144. They ramp in phase. This increases the effective buckconverter inductance. Hence, the current Icoil (L1) 312 under thein-phase coupling ramps slower than the current Icoil (L1) 314 that hasno coupling. It is noted that the current Icoil (L1) 312 has greaterarea underneath it than the current Icoil (L1) 314. It implies that theenergy delivered under the coupling case is higher than the energydelivered without the coupling. This justifies why the efficiency ishigher in the “sleep mode”.

Referring now to FIG. 4, it is one example diagram of the currents inthe inductor L1 142 and inductor L2 144 in the “sync mode” where thelarger transient response is needed. In this mode, the current Icoil(L1) 412 in the inductor L1 142 is out-of-phase with the current Icoil(L2) 422 in the inductor L2 144. Hence, they ramp out of phase. Thisdecreases the effective buck converter inductance. Hence, the currentIcoil (L1) 412 under the out-of-phase coupling ramps faster than thecurrent Icoil (L1) 414 that has no coupling. It implies that the buckconverter 100 under the coupling case responses faster to the load stepthan the case without the coupling. This justifies why better loadtransient response can be achieved in the “sync mode”.

The proposed embodiment can be implemented in exactly the opposite way.The polarity of the coupled coils 140 can be reversed. As a result, the“sleep mode” will be invoked when the output 132 and 134 are out ofphase while the “sync mode” will be invoked when the output 132 and 134are in phase.

Referring now to FIG. 5, it shows one example of the calculatedefficiency of the buck converter 100 from the proposed embodiment. Theefficiency 512 vs. the load current shows the efficiency of the buckconverter 100 when it is working in the “sleep mode” with the mutualinductance L12 146 equal to 1.2 uH. The efficiency 514 vs. the loadcurrent shows the efficiency of the buck converter 100 when it isworking in the “sleep mode” with the mutual inductance L12 146 equal to0.8 uH. The efficiency 522 vs. the load current shows the efficiency ofthe buck converter 100 when it is working in the “sync mode” with themutual inductance L12 146 equal to 1.2 uH. The efficiency 524 vs. theload current shows the efficiency of the buck converter 100 when it isworking in the “sync mode” with the mutual inductance L12 146 equal to0.8 uH. The improvement of the efficiency in the “sleep mode” has 1% forthe same load transient response. The decrease in “sync mode” efficiencyis negligible for significant load currents. FIG. 5 has been verifiedboth experimentally and in simulation. Hence, the proposed embodiment isconfirmed to be effective.

Referring now to FIG. 7, it shows the flowchart of the methodology ofusing the weakly coupled inductive coils to achieve both speed andefficiency from the proposed embodiment. It begins with the load leveljudgment 702. If the load is low, the sleep mode will be invoked through710. Then the weakly coupled inductive coils 140 will be fed by thein-phase control signals. Large equivalent inductance will be achieved.Then the generate bulk output at 730 will have very good efficiency. Ifthe load is high, the sync mode will be invoked through 720. Then theweakly coupled inductive coils 140 will be fed by the out-of-phasecontrol signals. Less equivalent inductance will be achieved. Then thegenerate bulk output at 730 will have better response speed. At theoutput of the bulk 730, a sample of the output will be taken through740. The sampled load information will be fed to the input of 702.

Referring now to FIG. 1, it shows one example when the multi-phaseswitches 110 contains only two pairs of complementary switches. One pairincludes the switches SW11 124 and SW12 126. Another pair includes SW21128 and SW22 130. However, the proposed embodiment can be extended tomore pairs in the multi-phase switches 110. For example, there can befour pairs of complementary switches in the multi-phase switches 110. Asa result, the buck converter 100 becomes a four-phase converter. In thePFM mode, the four phases are typically in phase (in the “sleep mode”)to achieve the maximum efficiency. But in the “sync mode”, the phaseswould typically be equally spaced with 0, 90, 180, and 270 degreedelays. The phases would therefore be paired as 0, 90, 180, and 270degree.

In the proposed embodiment, the coupled coils 140 can be extended toinclude more than one pair of coupled inductances L1 142 and L2 144. Thedrive scheme with different phases can be applied together with thecombination of many pairs of coupled coils to adjustable efficiency andload transient response. It shall be able switch to achieve the maximumeffective inductance for a high efficiency mode and or the fast responsefor the low output mode.

An alternative embodiment is to disable one phase. If a phase isdisabled, then the output of the disabled phase may be set to gohigh-impedance. In this case the voltage on the secondary coil—the oneon the disabled phase—may vary with the voltage on the primary coil.Thus the primary coil will act like a simple uncoupled inductor. Forthis embodiment, preferably, both phases through the one pair of coupledinductances L1 142 and L2 144 can be driven out-of-phase in the “syncmode” to minimize the effective capacitance. Then in the “sleep mode”the secondary phase can be disabled. Consequently the effectiveinductance will rise back to the nominal (uncoupled) value. This willincrease the efficiency.

Referring now to FIG. 2, a circuit schematic diagram illustrate oneexample of the variable efficiency and response buck converter 200 usingthe control unit 210, the phase control units 212 and 214, and theoutput monitor 230 with one embodiment of the disclosure. The circuit200 could be on a mobile device, such as a cellular phone, or on anintegrated circuit chip, such as CPU. The system 200 includes a controlunit 210, the phase control units 212 and 214, the output monitor 230,the multi-phase switches 216, the coupled coils 222, the filter cap 224,and the load resistor R_(L) 226. The control unit 210 generates phasecontrol signals 252 and 254 based on the pulse frequency modulation(PFM) or the pulse width modulation (PWM) need. The control unit 210 isalso preferably coupled to the input V_(MNT) 234 from the output monitorcircuit 230. The output 252 and 254 from the control unit 210 arecoupled to the two phase control units 212 and 214 respectively. Thephase control unit I 212 generates complementary analog signals 262 and264 coupled to the multi-phase switches 216. The phase control unit II214 generates complementary analog signals 266 and 268 coupled to themulti-phase switches 216. The multi-phase switches 216 includes at least2 pairs of complementary switches (the upper switch and the low switch).If there are only 2 pairs of complementary switches in the multi-phaseswitches 216, the phase output 272 and 274 are coupled to the input ofthe coupled coils 222. The coupled coils 222 includes at least a pair ofweakly coupled inductive coils. The output 240 of the coupled coils 222is preferably coupled to the filter capacitor 224. The filter capacitor224 and the load resistor R_(L) 226 are in parallel. The output voltageVout 228 is coupled to the load resistor R_(L) 226. The output voltageVout 228 is preferably coupled to the input V_(FB) 232 of the outputmonitor 230. The output monitor 230 monitors the output voltage Vout 228or the load current Iout 242 and generates the control signal V_(MNT)234 coupled to the control unit 210.

In the embodiment, the control unit 210 contains the circuit forautomatically switching between PWM and PFM modes based on the inputV_(MNT) 234 coupled from the output monitor 230. The output monitor 230includes a reference generator to generate the reference signal for theerror amplifier. The error amplifier generates the error signal betweenthe feedback signal V_(FB) 232 from the circuit output and the referencesignal. The error signal is coupled to the control unit 210 to decidewhich of the PWM and PFM modes will be used.

The number of the coupled coils 222 can be more than one.Correspondingly the multi-phase switch 216 coupled to the inputs of thecoupled coils can be more than one. The number of the multi-phase switch216 will be equal to the number of the coupled coils 222. Consequentlythere will be more the phase control units 212 and 214. The number ofthe phase control unit is equal to the 2 times of the multi-phase switch216.

As such, a novel variable efficiency and response buck converter withweakly coupled coils are herein described. The circuit uses the mutuallycoupled coils in a multi-phase switching converter to effectivelyachieve an electrically tunable inductance for energy storage, and totune the inductance according to whether a low inductance is desired forthe fast converter response, or a large inductance to suppress thecurrent ripple.

The device and method are applicable to a variety of programmable buckconverters and buck schemes. The device and method are extensible to addmore pairs of coupled coils and more multi-phase switches. Otheradvantages will be recognized by those of ordinary skill in the art.

The above detailed description of the disclosure, and the examplesdescribed therein, has been presented for the purposes of illustrationand description. While the principles of the disclosure have beendescribed above in connection with a specific device, it is to beclearly understood that this description is made only by way of exampleand not as a limitation on the scope of the disclosure.

What is claimed is:
 1. A variable efficiency and transient responsevoltage conversion circuit device, the device comprising: a convertercontrol unit; an array of phase control circuit units controlled by theconverter control unit; a multi-phase switch controlled by the array ofphase control circuit units; a mutually coupled inductive coil at theoutput of the multi-phase switch; a plurality of capacitors andresistors circuits at the output of the coupled inductive coil; and anoutput monitor circuit connected to the output of the plurality ofcapacitors and resistors circuits and the input of the converter controlunit.
 2. The device of claim 1 wherein the converter control unit iscapable of receiving control commands and transferring them into phasecontrol signals needed for phase control circuits, the converter controlunit further comprising: a circuit accepting control signals forefficiency and response specifications; and a regulation circuitaccepting signals from the output monitor circuit.
 3. The device ofclaim 1 wherein the array of phase control units connected to thecontrol unit is capable of converting signals from outputs of thecontrol unit to analog complementary control signals, each phase controlcircuit unit further comprising: a circuit accepting control signalsfrom the converter control unit; and a conversion circuit with certainembedded algorithms to implement complementary phase control signals. 4.The device of claim 1 wherein the multi-phase switch controlled by thearray of phase control circuit units is capable of creating an array ofcomplementary phase signals that enables sleep modes, sync modes, orother multi-phase modes according to the number of input complementaryphase control signals, a multi-phase switch further comprising: at leasttwo pairs of complementary signals as the input to multi-phase switches;at least two pairs of complementary switches receiving complementarysignals as inputs to generate sync mode or sleep mode complementaryphases; and at least one pair of phase signals generated as the outputfrom complementary switches.
 5. The device of claim 1 wherein themutually coupled inductive coil connected to output phase signals ofmulti-phase switches is capable of enabling both strong and weakcouplings to optimize efficiencies and speed requirements of switches,the mutually coupled inductive coil further comprising: 2 inductors withmutual couplings for 0° and 180° phases; or 4 inductors with mutualcouplings for 0°, 90°, 180°, 270°; or multi-inductors with more phases.6. The device of claim 1 wherein the plurality of capacitors andresistors circuits at an output of the coupled inductive coil arecapable of filtering out high frequency harmonics to deliver relativelyconstant voltages, a plurality of capacitors and resistors circuitsfurther comprising: a plurality of capacitors shunt in between theoutput and the common reference; a plurality of resistors shunt inbetween the output and the common reference; or a plurality ofcapacitors and resistors shunt in between the output and the commonreference.
 7. The device of claim 1 wherein the output monitor circuitconnected to the output of the plurality of capacitors and resistorscircuits and the input of the converter control unit is capable ofdetecting the load voltage or current and feed back the control signalinto the control unit for the pulse frequency modulation (PFM) or thepulse width modulation (PWM), the output monitor circuit furthercomprising: a high impedance receiving circuit to sample the loadcurrent or voltage; a signal conversion circuit with embedded algorithmsto transfer the sampled load current or voltage into control signals;and an output driving circuit to port the generated port signal into theconverter control unit to facilitate the pulse frequency modulation(PFM) or the pulse width modulation (PWM).